The production of ammonium polyphosphates for use as flame-retarding agents, especially in intumescent paints, has materially increased over the past few years. These ammonium polyphosphates range from water-soluble materials, through amorphous glasses, to crystalline, water-insoluble powders and have been produced utilizing a myriad of different procedures.
Ammonium polyphosphates can be represented by the generic formula EQU H.sub.(n.sub.-m).sub.+2 (NH.sub.4).sub.m P.sub.n O.sub.3n.sub.+1
wherein n is an integer having an average value greater than 10, m/n is between about 0.7 and about 1.1 and the maximum value of m is equal to n+2.
They are generally produced by a variety of different reactions including, but not limited to, those set forth by the following equations wherein APP represents ammonium polyphosphate. EQU (I) NH.sub.3 + H.sub.3 PO.sub.4 + H.sub.2 NCONH.sub.2 .fwdarw. APP EQU (ii) nh.sub.3 + h.sub.3 po.sub.4 + p.sub.2 o.sub.5 .fwdarw. app EQU (iii) nh.sub.4 oh + nh.sub.3 + pocl.sub.3 .fwdarw. APP EQU (iv) h.sub.3 po.sub.4 + h.sub.2 nconh.sub.2 .fwdarw. app EQU (v) (nh.sub.4).sub.4 p.sub.2 o.sub.7 + p.sub.2 o.sub.5 .fwdarw. app
these ammonium polyphosphates have been found useful, as mentioned above, as flame-retardant additives in the production of intumescent paints. They also impart flame-retardance to plastics, textiles and the like when incorporated therein.
More recently, it has been found that ammonium polyphosphates in general, and crystalline, water-insoluble ammonium polyphosphates in particular, can advantageously be incorporated into wood particleboard in order to impart flame-retardance thereto. Not only do the crystalline, water-insoluble ammonium polyphosphates impart flame-retardance to the board but they also do so to the same degree as other, more widely used, flame-retardant additives and, in most instances, at lesser concentrations.
In exploring the effects of ammonium polyphosphates upon the flame-retardance of particleboard and in assessing the many different variables which exist in the process of flame-proofing particleboard with polyphosphates, we have discovered that the pH of the ammonium polyphosphate plays an important role. The pH of the polyphosphate, the pH of the resinous glue which is used to bind the wood particles together during heat and pressure consolidation and the pH of the wood particles per se are all important variables which must be considered by the particleboard manufacturer. We have found that if the pHs of the melamine polyphosphate, the resin glue and the wood chips are all substantially identical, i.e. matched to within 0.5 units of one another, not only does the polyphosphate function normally as a flame-retardant but it effects the curing rate of the resinous glue. That is to say, a polyphosphate of too low a pH accelerates the resin cure and thereby results in boards having inferior properties of internal bond, delamination and surface quality, especially with urea-formaldehyde resins, the most widely used resins for glueing in particleboard production. However, since the pH of ammonium polyphosphates tends to fluxuate widely depending upon the starting materials charged and the method used in the production thereof, it became necessary to be able to produce ammonium polyphosphates of a controlled or desired pH since the pH of the wood chips and that of the resin glue in particleboard production are relatively constant.